1. Field of the Disclosure
Embodiments of the present disclosure relate to switching power supplies.
2. Description of Related Art
Transistors, such as metal oxide semiconductor field effect transistors (MOSFETs) are widely used in modern switching power supplies. Typically, a control circuit which generates a square wave signal is used to drive the MOSFET. The square wave signal alternates regularly between two levels: a high level and a low level. When the high level is applied to the MOSFET, the MOSFET is turned on. When the low level is applied to the MOSFET, the MOSFET is turned off. The ratio of the duration of the high level to that of the low level, namely, the pulse duration ratio, determines the output voltage of the switching power supply. The greater the pulse duration ratio, the greater the output voltage is.
Typically, a feedback circuit is utilized to feedback the output voltage to the control circuit. The control circuit adjusts the pulse duration ratio automatically according to the feedback voltage. However, when the feedback circuit is broken or damaged, the feedback signal may be incorrect. As a result, the pulse duration ratio may be too great to give the wrong output voltage, and may even damage the MOSFET.
Therefore, a switching power supply having an improved driving circuit for a transistor is needed to address the aforementioned deficiency and inadequacies.